1. Field of the Invention
The present invention relates to an insulated wire having good lubricity and resistance to processing such as winding of magnet wires.
2. Description of the Related Art
It is desirable for a coil to be miniaturized having a high efficiency and a larger number of insulated wires packed into a limited space and increased performances of equipments. Therefore, the coatings of the insulated wires are easily damaged by the needles of automated coil winding machines. The insulated wires often suffer from layer-to-layer short or ground failure. Attempts have been made to prevent the damage to coatings by decreasing a friction coefficient on the surfaces of the insulated wires. In one example, a lubricant such as a wax is coated on the surface of the insulated wire.
However, it is difficult for the above method to apply a uniform coating of the lubricant over the surface of the insulated wire. Furthermore, the insulated wires which are coated with the lubricant should be washed with solvents since the coated lubricants easily gathers dust or foreign particles.
Imparting lubricity to the insulated wires by adding lubricants (e.g. polyethylene, polytetrafluoroethylene, molybdenum disulfide, boron nitride, waxes, etc.) to a varnish for the insulating coating has been investigated.
However, it is extremely difficult to disperse the lubricants homogeneously in the varnish for the insulating coating, since the lubricants are insoluble or hardly soluble in the solvents. Therefore, problems arise such as wire breakage or poor appearance due to the nonuniformity of the insulating coating in the production step of insulated wires.
The wire breakage and poor appearance have been solved by the selection of lubricants and adjustment of the added amount of lubricants, but the obtained insulated wires have insufficient lubricity.
In particular, the above problems are significant when the lubricants are added to polyamideimide or polyimide which is a heat resistant insulating coating resin. Therefore, the heat resistant insulated wires having the coating of polyamideimide or polyimide which has good lubricity have not been produced.